Among plastics, a thermosetting resin exhibits excellent electrical insulation, heat resistance and mechanical strength. Therefore, the thermosetting resin has been widely used as a material for electric and electronic parts, automobile parts or the like.
When a thermosetting resin is once cured, it is not dissolved in a solvent either without being softened and melted due to heat. Accordingly, it has been technically difficult to regenerate a valuable chemical raw material from a cured product thereof. However, the need of environmental preservation and building of a recycling based society has been reviewed these days, and various researches on recycling of thermosetting resins have been made.
In order to overcome these problems, Patent Document 1 discloses a technology in which, while a phenol resin is dissolved in phenol that is a constituent monomer of the resin to decompose to a low molecular compound such as phenol or the like, an organic filler is recovered.
Furthermore, Patent Document 2 discloses a technology in which alcohol in a supercritical state or subcritical state is brought into contact with a phenol resin to decompose to and recover phenol. Patent Document 2 further describes to the effect that a phenol resin may be produced through a reaction of the recovered phenol with formaldehyde.
However, according to the technologies of Patent Documents 1 and 2, the yield rate of the recycled thermosetting resin is not excellent.
In Patent Document 3, when the molecular weight distribution of an oligomer obtained by decomposing a thermosetting resin in a supercritical or subcritical state solvent becomes constant, recycle of the thermosetting resin has been carried out with the addition of a multi-functional compound. In this way, the quality of the recycled resin can be stabilized.
Furthermore, there has also been known a technology for improving the decomposition efficiency of the aforementioned thermosetting resin. In Patent Document 4, there has been disclosed a technology for mixing a thermosetting resin with a dispersing agent comprising a reaction solvent and a phenol resin to obtain a slurry. Accordingly, there has been disclosed that the stable high decomposition rate may be achieved by suppressing aggregation and sedimentation of a solid content in a high concentration slurry.
Furthermore, Patent Document 5 discloses that a phenol resin molding material having excellent mechanical strength is obtained with the use of a decomposed residue by adding a step of adjusting the decomposed residue containing an inorganic filler of the aforementioned thermosetting resin to a specific range.